Checking for a null entry in a textbox

Checking for a null entry in a textbox

• MAPIdoneit

  Hope you will bear with me.

  >in c# you can assign a textbox's text to null but it doesn't actually stay a null value.

  I am not trying to assign a textbox's text to a null. I am trying to find out if it is already null. I assume if no data has been entered into it, such is the case. How do I do this

  Are you saying that if noone has yet entered data into the textbox that it will = "" anyway.

  If so, fine. I don't understand why and I would appreaciate it if someone would explain it to me, but if this is the case at least that solves the problem.

  
  
  

  
  

• GhadaKamel

  in c# you can assign a textbox's text to null but it doesn't actually stay a null value.   The property will assign the text to be "" if it's assigned to null.  Also "" is not equal to null
  
  textBox1.Text = null;
  
  if( textbox1.Text == null)
  // will not ever hit this...
  else if ( textbox.Text == "")
  // instead it will be an empty string and hit this
  
  The only way to check if someone has typed something in is to write code to handle the TextChanged event or the Validating event if checking if the text == "" is not good enough.
  
  

• Jster

  Like Alan says:

   

  You cannot check textBox1.Text for being a true NULL.

   

  textBox1.Text is a String and String types can never be NULL.

   

  Behind-the-scenes, a String is just a sequence of Unicode characters.

   

  An “empty” textBox1.Text is a string that looks empty or null but it really has a 1 character sequence, /0.

   

  Your quote-quote(“”) is also a string that looks empty or null, but it also really has a 1 character sequence, /0.

   

  So, when you do this: if (textBox1.Text == “”),  the system will see that both textBox1.Text and “” really contain the same character sequence(/0), and will report to you that they are equal.

  
  

• JainNitin

  So you're saying that this is something that C# handles differently that VB. If so, That's fine. I'm not complaining, just need to understand.

  To summarize: When a textbox is put on a form and you run the form, if no value has been entereed into the textbox and you check for its value it is not going to be null, but rather "". Is this correct

  
  

• Gutenberg

  You could try String.IsNullOrEmpty(<string>). Works for me anyway

  Example
  if(String.IsNullOrEmpty(TextBox.Text))
  ...do something interesting...

  http://msdn2.microsoft.com/en-us/library/system.string.isnullorempty(d=ide).aspx

  
  

• SonaliC

  Does C# consider "" as a null In VB you can move to a text box, put something in it, take it out again and the value of the textbox will be "". But if you've never put data into the textbox at all it is considered a null and its value is something else (nothing as I remember it or maybe it's dbNull, can't remember).

  In C# does "StrValue = textbox1.text" check for a true null or an empty string

  
  

• D_S_Clark

  This is correct. When a textbox is created (textbox.Text == "") is true. It is different from VB.
  
  The only reason I showed the assignment was to show you that the string can never be null, and was supposed to also imply at creation.
  
  

• mohammedAhmed_1978

  hi am new to vb and I was wondering about this as well I basically want to make it so that when the user clicks a radio button and the text box has no text nothing happens. if there is text in the text box everything works as it should.  here is the code

   

  ---

  Public Class Form1

  Private Sub RadioButton1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles RadioButton1.Click

   If Me.RadioButton1.Checked Then PictureBox1.Image = PictureBoxSunny.Image

  With Me

  With .TextBox2

  'Clear the text box

  .Clear()

  'Reset focus

  .Focus()

  End With

  .TextBox2.Clear()

  End With

  With Me

  .TextBox2.Text = .TextBox1.Text & ", today is going to be Sunny. " & .TextBox2.Text

   End With

  End Sub

   Private Sub RadioButton2_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles RadioButton2.Click

  If Me.RadioButton2.Checked Then PictureBox1.Image = PictureBoxSnowy.Image

  With Me

  With .TextBox2

  'Clear the text box

  .Clear()

  'Reset focus

  .Focus()

  End With

  .TextBox2.Clear()

  End With

   With Me

  .TextBox2.Text = .TextBox1.Text & ", today its going to Snow. " & .TextBox2.Text

   End With

  End Sub

  Private Sub RadioButton3_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles RadioButton3.Click

  If Me.RadioButton3.Checked Then PictureBox1.Image = PictureBoxRainy.Image

  'Clear the previous text

  With Me

  With .TextBox2

  'Clear the text box

  .Clear()

  'Reset focus

  .Focus()

  End With

  .TextBox2.Clear()

  End With

  With Me

  .TextBox2.Text = .TextBox1.Text & ", today its going to Rain. " & .TextBox2.Text

   End With

  End Sub

  Private Sub RadioButton4_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles RadioButton4.Click

  If Me.RadioButton4.Checked Then PictureBox1.Image = PictureBoxCloudy.Image

  'Display the name that was typed into the first textbox along with a message into the second textbox

  With Me

  With .TextBox2

  'Clear the text box

  .Clear()

  'Reset focus

  .Focus()

  End With

  .TextBox2.Clear()

  End With

   With Me

  .TextBox2.Text = .TextBox1.Text & ",today is going to be Cloudy." & .TextBox2.Text

   End With

  End Sub

  Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

  With Me

  With .TextBox1

  'Clear the text box

  .Clear()

  'Reset focus

  .Focus()

  End With

  .TextBox1.Clear()

  .TextBox2.Text = ""

  End With

  End Sub

   End Class

   

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• Checking for a null entry in a textbox